With the recent increased interest in mid-wavelength infrared (hereinafter referred to as “MWIR”) optoelectronic devices and applications, much attention has been directed to semiconductor optoelectronic devices, such as lasers, light emitting diodes (hereinafter referred to as “LEDs”), photodetectors, photodiodes, or the like. Particular concern has been directed to the area of lasers that operate at wavelengths between approximately 2 μm and 6 μm. Such devices are essential components in optical systems, which may be used for applications including remote sensing, LADAR, detection of chemical warfare agents, intelligence, surveillance and reconnaissance (ISR), enemy missile tracking and infrared countermeasures (IRCM).
An example of one such device is an edge-emitting laser (hereinafter referred to as an “EEL”), which may be used to provide a light signal in the above-mentioned optical systems. EELs typically include upper and lower contacting and cladding regions, formed on opposite sides of an active region. The EEL may be driven or pumped electrically by forcing current through the active region or optically by supplying light of a desired frequency to the active region.
In conventional telecommunication and data-communication EELs, typical device structures perform adequately. However, for MWIR applications, it is typically difficult to form structures with both good optical performance and, simultaneously, good electrical performance.
It is generally desirable to provide an EEL device with improved conductive regions that provide current flow through the active region of the device. Current flow is typically achieved by including highly doped layers in the EEL, on either side of the active region, allowing a high vertical current flow. However, sufficiently high doping levels can be difficult to achieve for some semiconductor materials used in MWIR devices, causing undesirable effects on current flow. In particular, n-type doping of InGaAlSb layers is a key problem in the realization of MWIR devices. It is difficult to achieve high electron concentrations in many compositions of this alloy since the ionization energy can be relatively high. Without adequate current flow, resistivity of devices increases and current injection can be non-uniform or exhibit current crowding effects, problems which can degrade optoelectronic device performance. Furthermore, growth of some semiconductor materials required for forming conductive regions is limited by the miscibility gap.
It would be highly advantageous, therefore, to remedy the foregoing and other deficiencies inherent in the prior art.